The Contribution of Electrons to the Sputter-produced O2 Exosphere on Europa

Electrons contribute a strong radiation component to the surface bombardment of Europa. However, they are not typically considered to contribute to erosion of the surface H2O-ice or produce exospheres of radiolytic O-2, as laboratory studies on sputtering induced by electrons are sparse. Here we have measured the sputtering yield of H2O-ice induced by 0.5 keV electrons between 14 and 125 K, estimating the composition of the stable products ejected during irradiation. Combining these measurements with updated electron flux measurements, we estimate for the first time that the global surface production rate of O-2 from electron-induced sputtering is larger than the production rate previously estimated for all of the ionic components combined. Our results emphasize the importance of electrons in producing exospheres on icy satellites and suggest that these exospheres need not be tied to environments where the surface is being bombarded with heavy ions.